Processing of substrates (e.g., semiconductor, glass, etc.) for use in electronic devices is typically done in one or more processing systems. Although multiple processing steps may be performed in a single processing system, substrates typically may be transported between processing systems for at least some of the processing steps.
Substrates generally are stored in cassettes or pods (hereinafter referred to collectively as “substrate carriers”) for transfer from one processing system to another, and between processing systems and other locations, such as storage locations. Although substrate carriers may be carried manually between processing systems, the transfer of substrate carriers is typically automated. For instance, automatic handling of a substrate carrier may be performed by a transfer robot or vehicle, which may deliver and retrieve substrate carriers from the load port of a process tool. The transfer robot or vehicle may be part of an overhead transport system (OHT system). Any suitable Automated Material Handling System (AMHS) may be used. Conventionally, the transfer robot and the process tool load port are independently controlled. More specifically, typically the robot or vehicle is controlled by the OHT system, and the process tool load port is controlled by the process tool. As such, the process tool and OHT system typically perform a communication handshake, i.e. exchange of communication signals before, during, and after the transfer of a substrate carrier. This handshake may ensure that both entities are prepared for the transfer and perform the correct actions for safe transfer of the substrate carrier. For example, in semiconductor factories, the SEMI E84 standard is typically used for the substrate carrier handoff interface, which may enable safe exchange of the substrate carriers between the transfer robot or vehicle of the OHT system and the process tool load port. The conventional SEMI E84 protocol requires the transfer robot or vehicle to arrive at the process tool load port of the process tool ready to perform a transfer, and then begin the handshake protocol with the process tool. After the handshake protocol has begun, the process tool may accept the transfer and subsequently the transfer robot may then transfer the substrate carrier to/from the load port of the process tool. Alternatively, the process tool may reject the transfer and subsequently the transfer robot or vehicle may abort the transfer. However, a need exists for improved methods and apparatus for substrate carrier handoff.